The Hopkins Population Center (HPC) requests a five-year renewal, for years 24 to 28, of its NICHD P30 Population Research Center Core Grant. The HPC has a long and distinguished record as a research center focusing on both domestic and international population issues. Population research at Hopkins, dating back to the 1930s, has always had a distinctive public health perspective, linking biological science to behavioral science, and taking results from the laboratory onto the street. Today, the HPC supports research throughout the University on population-related topics as diverse as the impact of welfare reform on families, the effects of needle-sharing networks on the spread of sexually-transmitted disease (STDs), development of a barrier method of female contraception that would also protect against STDs, and the manner in which cells in the mammalian testis communicate with each other. The HPC is administratively located in the Johns Hopkins School of Hygiene and Public Health, among the preeminent centers for public health research and teaching in the world. The School of Hygiene and Public Health provides a behavioral and biological science link between the Medical School and the social science departments in the School of Arts and Sciences. The HPC facilitates and fosters research connections within and between these divisions of the University through the provision of essential research infrastructure. Continuation of P30 support for the Center for the period 1997-2002 will allow us to maintain the existing infrastructure offered to Center associates, to expand the range of services offered and to accommodate the expected increase in numbers of associates over the next five years. This proposal requests support for seven Cores: (1) Administration; (2) Computing; (3) Information Services; 94) Quantitative Sciences; (5) Sexually Transmitted Disease Diagnostics; (6) Morphology; and (7) Radioimmunoassay. Over the grant period, the HPC proposes to take advantage of rapidly-evolving technology and recent faculty appointments to expand and improve the Center's cores, and to increase integration and communication among them.